Buffer layers on metal surfaces having biaxial texture as superconductor substrates

ABSTRACT

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y 2  O 3  /Ni, YSZ/Y 2  O 3  /Ni, RE 2  O 3  /Ni, (RE=Rare Earth), RE 2  O 3  /Y 2  O 3  /Ni, RE 2  O 3  /CeO 2  /Ni, and RE 2  O 3  /YSZ/CeO 2  /Ni, Y 2  O 3  /Cu, YSZ/Y 2  O 3  /Cu, RE 2  O 3  /Cu, RE 2  O 3  /Y 2  O 3  /Cu, RE 2  O 3  /CeO 2  /Cu, and RE 2  O 3  /YSZ/CeO 2  /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approaches, which include chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

The United States Government has rights in this invention pursuant tocontract no. DE-AC05-96OR22464 between the United States Department ofEnergy and Lockheed Martin Energy Research Corporation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a Continuation-in-Part of pending U.S. patentapplication Ser. No. 09/096,559 Buffer Layers on Rolled Nickel or Copperas Superconductor Substrates filed on Jun. 12, 1998 by Paranthaman etal.

The present invention relates to issued U.S. Pat. No. 5,741,377"Structures Having Enhanced Biaxial Texture and Method of FabricatingSame" by Goyal et al., filed Apr. 10, 1995 and issued Apr. 21, 1998; topending U.S. patent application Ser. No. 08/670,871 "High Tc YBCOSuperconductor Deposited on Biaxially Textured Ni Substrate" by Budai etal., filed Jun. 26, 1996; and also to U.S. Patent Application "MgOBuffer Layers on Rolled Nickel Superconductor Substrates," byParanthaman et al., Docket Number ERID 0218, filed on Jun. 12, 1998, allof which are hereby incorporated in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to structures upon which high currentconductors may be epitaxially deposited on biaxially-textured rolledsubstrates of nickel and/or copper and other metals and alloys which canbe characterized by a surface having biaxial texture. Also described aremethods for fabricating said structures. The structures and methods formaking the structures include but are not limited to Y₂ O₃ /SS(SS=Substrate comprising at least one metal and having a surfaceexhibiting biaxial texture), YSZ/Y₂ O₃ /SS (YSZ=yittria-stabilizedzirconia), RE₂ O₃ /SS (RE=Rare Earth), RE₂ O₃ /Y₂ O₃ /SS, Y₂ O₃ /CeO₂/SS, RE₂ O₃ /Ce₂ O₃ /SS, Y₂ O₃ /YSZ/CeO₂ /SS, RE₂ O₃ /YSZ/CeO₂ /SS, and(RE')_(x) O_(y) /SS (RE'=any combination which includes, but is notlimited to Rare Earth elements, wherein x is a value near 2.0, believedto be between about 1.95 and about 2.05, (hereinafter stated as about2.0), and wherein y is between about 3.0 and about 3.7).

BACKGROUND OF THE INVENTION

It has long been desired to grow biaxially oriented oxide buffer layersother than CeO₂ directly on textured substrates, and also to have asingle buffer layer on textured substrates. Also it has been desired toprovide an alternative to pulsed laser deposition processes that may beeasier to scale up for producing long length substrates.

Recent developments in deposited conductors, both rolling assistedbiaxially textured substrates (RABiTS), and ion-beam assisted deposition(IBAD) based on YBa₂ Cu₃ O₇ superconductors are promising, and areherein reported for the first time.

The "deposited conductor" approach described herein is useful forgrowing superconductors such as REBa₂ Cu₃ O₇, (Bi,Pb)₂ Sr₂ Ca_(n-1)CunO_(2n+4) (n=1-3), TlBa₂ Ca_(n-1) Cu_(n) O_(2n+3) (n=1-4), Tl₂ Ba₂Ca_(n-1) Cu_(n) O_(2n+4) (n=1-3), and Hg₁ Ba₂ Ca_(n-1) Cu_(n) O_(2n+2+)δ(n=1-4) with high critical-current densities. These high J_(c)conductors will be suitable for transmission lines and various otherapplications. The demonstrated buffer layers may also be useful forphotovoltaics, ferroelectrics, sensors, and electro-optic applications.

The following sections of publications also relate to the presentinvention, and are hereby incorporated by reference:

X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H.Campbell, P. Tiwari, Y. Coulter, and D. E. Peterson, Appl. Phys. Lett.65 (15), Oct. 10, 1994, pl961.

M. Paranthaman et al., Physica C 275 (1997) 266-272.

OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide new andimproved biaxially oriented oxide buffer layers other than CeO₂ directlyon textured-Ni and/or Cu substrates.

It is another object to provide an alternative to pulsed laserdeposition processes as well as improved buffer layer architectures thatmay be easier to scale up for producing long length substrates.

Further and other objects of the present invention will become apparentfrom the description contained herein.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, the foregoingand other objects are achieved by a biaxially textured article whichcomprises a substrate comprising at least one metal, the substratehaving a surface exhibiting biaxial texture; and a buffer layer selectedfrom the group consisting of Y₂ O₃ and RE₂ O₃, the buffer layer beingepitaxially disposed upon the biaxially-textured surface of thesubstrate.

In accordance with a second aspect of the present invention, theforegoing and other objects are achieved by a biaxially textured articlewhich comprises a substrate comprising at least one metal, the substratehaving a surface exhibiting biaxial texture; a first buffer layercomprising CeO₂, the first buffer layer being epitaxially disposed uponthe biaxially textured surface of the substrate; and a second bufferlayer selected from the group consisting of Y₂ O₃ and RE₂ O₃, the secondbuffer layer being epitaxially disposed upon the biaxially texturedsurface of the CeO₂.

In accordance with a third aspect of the present invention, theforegoing and other objects are achieved by i biaxially textured articlewhich comprises a substrate comprising at least one metal, the substratehaving a surface exhibiting biaxial texture; a first buffer layercomprising CeO₂, the first buffer layer being epitaxially disposed uponthe biaxially textured surface of the substrate; a second buffer layercomprising YSZ, the second buffer layer being epitaxially disposed uponthe biaxially textured surface of the CeO₂ ; and a third buffer layerselected from the group consisting of Y₂ O₃ and RE₂ O₃, the third bufferlayer being epitaxially disposed upon the biaxially textured surface ofthe YSZ.

In accordance with a fourth aspect of the present invention, theforegoing and other objects are achieved by a biaxially textured articlewhich comprises a substrate comprising at least one metal, the substratehaving a surface exhibiting biaxial texture; and a buffer layercomprising (RE')_(x) O_(y), wherein x is about 2.0, and y is betweenabout 3.0 and about 3.7, the buffer layer being epitaxially disposedupon the biaxially textured surface of the substrate.

In accordance with a fifth aspect of the present invention, theforegoing and other objects are achieved by a method for making abiaxially textured article which comprises the steps of: providing asubstrate comprising at least one metal, the substrate having a surfaceexhibiting biaxial texture; and epitaxially depositing upon thebiaxially textured surface of the substrate a buffer layer selected fromthe group consisting of Y₂ O₃ and RE₂ O₃.

In accordance with a sixth aspect of the present invention, theforegoing and other objects are achieved by t method for making abiaxially textured article which comprises the steps of: providing asubstrate comprising at least one metal, the substrate having a surfaceexhibiting biaxial texture; epitaxially depositing upon the biaxiallytextured surface of the substrate a first buffer layer comprising CeO₂ ;and epitaxially depositing upon the biaxially textured surface of theCeO₂ a second buffer layer selected from the group consisting of Y₂ O₃and RE₂ O₃.

In accordance with a seventh aspect of the present invention, theforegoing and other objects are achieved by a method for making abiaxially textured article which comprises the steps of: providing asubstrate comprising at least one metal, the substrate having a surfaceexhibiting biaxial texture; epitaxially depositing upon the biaxiallytextured surface of the substrate a first buffer layer comprising CeO₂ ;

epitaxially depositing upon the biaxially textured surface of the CeO₂ asecond buffer layer comprising YSZ, and epitaxially depositing upon thebiaxially textured surface of the YSZ a third buffer layer selected fromthe group consisting of Y₂ O₃ and RE₂ O₃.

In accordance with an eighth aspect of the present invention, theforegoing and other objects are achieved by a method for making abiaxially textured article which comprises the steps of: providing asubstrate comprising at least one metal, the substrate having a surfaceexhibiting biaxial texture; and

epitaxially depositing upon the biaxially textured surface of thesubstrate a buffer layer comprising (RE')_(x) O_(y), wherein x is about2.0, and y is between about 3.0 and about 3.7.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of the various buffer layer architecturesdeveloped on textured-Ni and/or textured-Cu substrates.

FIG. 2 is the room temperature powder X-ray diffraction pattern for a100 nm thick Y₂ O₃ film grown on textured-Ni substrates by e-beamevaporation.

FIG. 3 is the Y₂ O₃ (222) pole figure for Y₂ O₃ films grown directly ontextured-Ni substrates by e-beam evaporation.

FIG. 4 is the room temperature powder X-ray diffraction pattern for a100 nm thick Yb₂ O₃ film grown on textured Ni substrates by e-beamevaporation.

FIG. 5 is an X-ray ω scan for a 100 nm thick Yb₂ O₃ -buffered Nisubstrates with FWHM of 11.7° for Yb₂ O₃ (400).

FIG. 6 is an X-ray φ scan for a 100 nm thick Yb₂ O₃ -buffered Nisubstrates with FWHM of 9.5° for Yb₂ O₃ (222).

FIG. 7 is the room temperature powder X-ray diffraction pattern for a400 nm thick YSZ film grown on Y₂ O₃ -buffered Ni substrates by rfmagnetron sputtering.

FIG. 8 is an x-ray ω scan for a 400 nm thick YSZ film grown on Y₂ O₃-buffered Ni substrates with FWHM of 9.5° for YSZ (200).

FIG. 9 is an X-ray φ scan for a 400 nm thick YSZ film grown on Y₂ O₃-buffered Ni substrates with FWHM of 11.7° for YSZ (220).

FIG. 10 is the room temperature powder X-ray diffraction pattern for a400 nm thick Yb₂ O₃ -film grown on Y₂ O₃ -buffered Ni substrates by rfmagnetron sputtering.

FIG. 11 is the room temperature powder X-ray diffraction pattern for Yb₂O₃ -films grown on CeO₂ -buffered Ni substrates by rf magnetronsputtering.

FIG. 12 is an X-ray ω scan for YBCO film on Yb₂ O₃ /CeO₂ -buffered Nisubstrates with FWHM of 7.7° for YBCO (006).

FIG. 13 is an X-ray φ scan for YBCO film on Yb₂ O₃ /CeO₂ -buffered Nisubstrates with FWHM of 9.5° for YBCO (103).

FIG. 14 is an X-ray ω scan for YBCO film on Yb₂ O₃ /YSZ/CeO₂ -bufferedNi substrates with FWHM of 6.5° for YBCO (006).

FIG. 15 is an X-ray φ scan for YBCO film on Yb₂ O₃ /YSZ/CeO₂ -bufferedNi substrates with FWHM of 8.9° for YBCO (103).

FIG. 16 is the temperature dependence resistivity plot for YBCO film onYb₂ O₃ /CeO₂ /Ni.

FIG. 17 is the temperature dependence resistivity plot for YBCO film onYb₂ O₃ /YSZ/CeO₂ /Ni.

FIG. 18 is the temperature dependence resistivity plot for YBCO film onYb₂ O₃ /Y₂ O₃ /Ni.

FIG. 19 shows the temperature dependance of normalized critical currentdensities of YBCO deposited on Yb₂ O₃ /YSZ/CeO₂ /Ni, Yb₂ O₃ /CeO₂ /Ni,and Yb₂ O₃ /Y₂ O₂ /Ni. Also included is the result of YBCO deposited onstandard YSZ/CeO₂ /Ni architecture for comparison.

FIG. 20 shows the magnetic field dependence of normalized criticalcurrent densities of YBCO deposited on Yb₂ O₃ /YSZ/CeO₂ /Ni and Yb₂ O₃/CeO₂ /Ni. Also included is the result of YBCO deposited on standardYSZ/CeO₂ /Ni architecture for comparison.

FIG. 21 shows the room temperature powder X-ray diffraction pattern fora 90-nm thick Gd₂ O₃ film grown on textured-Ni substrates by e-beamevaporation.

FIG. 22 is X-ray ω scans for a 90-nm thick Gd₂ O₃ -buffered Ni substratewith FWHM of 7.1° for Ni (200) and 5.2° for Gd₂ O₃ (400).

FIG. 23 is X-ray φ scans for a 90-nm thick Gd₂ O₃ -buffered Ni substratewith FWHM of 10.1° for Ni (111) and 9.2° for Gd₂ O₃ (222).

FIG. 24 is a pole figure for Gd₂ O₃ film grown directly on textured-Ni(222) substrate by e-beam evaporation.

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings.

DETAILED DESCRIPTION OF THE INVENTION

This invention describes how to grow biaxially oriented oxide bufferlayers other than CeO₂ directly on textured-Ni and/or Cu substrates andother metals and alloys which can be characterized by a surface havingbiaxial texture, and also describes methods for making buffer layers ontextured substrates. High rate depositions are accomplished by thedemonstrated reactive evaporation. Some of the buffer layers grown maybe excellent diffusion barriers for Ni and/or Cu and may be chemicallycompatible with the high temperature superconductors. This inventionalso demonstrates the possibility of having a single buffer layer ontextured-Ni and/or Cu substrates. This invention also demonstrates thepossibility of obtaining predominantly the single texture component ofYBCO superconductors. This invention opens up a wide variety ofpossibilities of growing several other buffer layers such as REAlO₃(RE=Rare Earth), AEZrO₃, (AE=Alkaline Earth, Ca,Sr,Ba), RE₂ Zr₂ O₇,Ca-stabilized Zirconia, Ti, Nb or Zr doped CeO₂, and AECeO₃ on eitherbuffered-rolled metal substrates or directly on rolled metal substrates.These buffer layers may be of interest to other areas likephotovoltaics, ferroelectrics, sensors and optoelectronic devices.

Buffer layers such as Y₂ O₃, RE₂ O₃, CeO₂, and YSZ were deposited onRABiTS by vacuum processing techniques such as electron-beam evaporationand rf magnetron sputtering. FIG. 1 summarizes the architectures ofvarious buffer layers developed in this invention.

The first buffer layer comprises an epitaxial laminate of Y₂ O₃, RE₂ O₃,RE₂ O₃ /Y₂ O₃ or YSZ/Y₂ O₃ deposited on a biaxially cube textured Niand/or Cu substrate. The crystallographic orientation of the Y₂ O₃, RE₂O₃, and YSZ were mostly (100). The second alternative buffer layercomprises an epitaxial laminate of Y₂ O₃ or RE₂ O₃ on CeO₂ -buffered Niand/or Cu substrates. The third alternative buffer layer comprises anepitaxial laminate of RE₂ O₃ (RE=Rare Earth)/YSZ/CeO₂ /Ni (or Cu). TheRE₂ O₃ films were grown epitaxially on YSZ-buffered Ni or Cu substrates.YBCO (YBa₂ Cu₃ O_(7-x)) has also been grown on some of the buffer layersby pulsed laser deposition. An estimated J_(c) of 0.7×10⁶ A/cm² at 77° Kand zero field for a film with the architecture YBCO/Yb₂ O₃ /CeO₂ /Ni. AJ_(c) of 1.4×10⁶ A/cm² at 77° K and zero field was also obtained forYBCO/Yb₂ O₃ /YSZ/CeO₂ /Ni, and a J_(c) of 0.8×10⁶ A/cm² at 77° K forYBCO/Yb₂ O₃ /Y₂ O₃ /Ni. The above-described buffer layers may also beuseful for the subsequent growth of superconductors such as REBa₂ Cu₃ O₇(RE=Rare Earth), (Bi,Pb)₂ Sr₂ Ca_(n-1) Cu_(n) O_(2n+4) (n=1-3), Tl₁ Ba₂Ca_(n-1) Cu_(n) O_(2n+3) (n=1-4), Tl₂ Ba₂ Ca_(n-1) Cu_(n) O_(2n+4)(n=1-3), and Hg₁ Ba₂ Ca_(n-1) Cu_(n) O_(2n+2+)δ (n=1-4) that arechemically and epitaxially compatible with Y₂ O₃, and RE₂ O₃ bufferlayers.

For purposes herein, the following definitions apply: Biaxial(ly)Texture: The films are oriented in both out-of-plane (along the (001)direction) and in plane (along the (100) direction) directions.Epitaxial(ly): The films grown on a particular substrate will grow inthe same orientation of the substrate is defined as epitaxial, forexample, cube-on-cube orientation. Thus, a buffer layer as describedherein as having been epitaxially deposited upon a biaxially-texturedsurface also exhibits a biaxially textured surface. RABiTS:Rolling-assisted biaxially-textured substrates; Rare Earth (RE): Thegroup of elements which consists of: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu. RE': any combination including but notlimited to Rare Earth elements. (RE')_(x) O_(y) : Any combinationincluding but not limited to Rare Earth oxides, especially wherein x isabout 2.0, and y is between about 3 and about 3.7.

YBCO: YBa₂ Cu₃ O_(7-x). YSZ: yttria-stabilized zirconia. Table 1summarizes the list of rare earth oxides and their structure type.

The specific processing conditions of the successful multi-layersequences are described in detail hereinbelow.

EXAMPLE 1 Growth of Y₂ O₃ on Textured-Ni and/or Cu Substrates by e-beamEvaporation

An electron beam (e-beam) evaporation technique was used to deposit Y₂O₃ films directly on Ni. The as-rolled Ni substrates were cleanedultrasonically with both acetone and methanol and recrystallized to thedesired (100) cube texture by annealing the substrates at 800° C. for 2hours in a vacuum of 10⁻⁶ Torr. Biaxially oriented Ni substrates weremounted on a substrate holder with a heater assembly in the e-beamsystem. After the vacuum in the chamber had reached 1×10⁻⁶ Torr at roomtemperature, a gas mixture of 4% H₂ and 96% Ar was introduced until thepressure inside the chamber reached 1 Torr. The Ni substrates wereannealed at 700° C. for 1 hour at that pressure. The chamber was thenpumped and maintained at a pressure of 2×10⁻⁵ Torr using a mixture of 4%H₂ and 96% Ar. The gas flow was controlled by a dc-powered piezoelectricvalve. The Y₂ O₃ layers were grown on the Ni substrates at temperaturesranging from 200 to 750° C. The deposition rate for Y₂ O₃ was 1-5 Å/secwith the pressure of 10⁻⁵ Torr, and the final thickness was varied from20 nm to 200 un. The crucibles used were mostly of tungsten. Yttriummetal was used as the source. The XRD results from the θ-2θ scan (asshown in FIG. 2), ω and φ scans for as-deposited Y₂ O₃ (20 nm thick) onNi at 700° C. are as follows: The strong Y₂ O₃ (200) from FIG. 2revealed the presence of a good out-of-plane texture. The FWHM for Ni(200) and Y₂ O₃ (200) are 7.2° and 7.1°, and that of Ni (202) and Y₂ O₃(222) are 11.7° and 8.4°, respectively. The Y₂ O₃ (222) pole figure forY₂ O₃ films grown at 700° C. on Ni is shown in FIG. 3. From the XRDresults, it can be concluded that Y₂ O₃ can be grown epitaxially on Ni.The CeO₂ was also grown epitaxially on textured-Ni substrates at about625° C. using Ce metal as the source.

The pulsed laser deposition technique was used to grow YBCO at 780° C.and 185 mTorr O₂ on all the buffered-Ni substrates.

The methods described in Example 1 can also be used to grow Y₂ O₃ ontextured-Cu substrates as well as on alloys of Cu and/or Ni and othermetals and alloys which can be characterized by a surface having biaxialtexture by e-beam evaporation.

EXAMPLE 2 Growth of Yb₂ O₃ on Textured-Ni and/or Cu Substrates by e-beamEvaporation

An electron beam (e-beam) evaporation technique was used to deposit Yb₂O₃ films directly on Ni. The as-rolled Ni substrates were cleanedultrasonically with both acetone and methanol and recrystallized to thedesired (100) cube texture by annealing the substrates at 800° C. for 2hours in a vacuum of 10⁻⁶ Torr. Biaxially oriented Ni substrates weremounted on a substrate holder with a heater assembly in the e-beamsystem. After the vacuum in the chamber had reached 1×10⁻⁶ Torr at roomtemperature, a gas mixture of 4% H₂ and 96% Ar was introduced until thepressure inside the chamber reached 1 Torr. The Ni substrates wereannealed at 650° C. for 1 hour at that pressure. The chamber was thenpumped and maintained at a pressure of 2×10⁻⁵ Torr using a mixture of 4%H₂ and 96% Ar. The gas flow was controlled by a dc-powered piezoelectricvalve. The Yb₂ O₃ layers were grown on the Ni substrates at temperaturesranging from 200 to 750° C. The deposition rate for Yb₂ O₃ was 1-5 Å/secwith the operating pressure of 10⁻⁵ Torr, and the final thickness wasvaried from 20 nm to 200 nm. The crucibles used were of graphite.Ytterbium oxide pellets were used as the source. The XRD results fromthe θ-2θ scan (as shown in FIG. 4), ω and φ scans (FIGS. 5 and 6) foras-deposited Yb₂ O₃ (100 nm thick), on Ni at 700° C. is as follows: Thestrong Yb₂ O₃ (400) from FIG. 4 revealed the presence of goodout-of-plane texture. The FWHM for Yb₂ O₃ (400) are 11.7°, and that ofYb₂ O₃ (222) is 9.5° respectively. From the XRD results, it can beconcluded that Yb₂ O₃ can be grown epitaxially on Ni.

The methods described in Example 2 can also be used to grow Yb₂ O₃ ontextured-Cu substrates as well as on alloys of Cu and/or Ni and othermetals and alloys which can be characterized by a surface having biaxialtexture by e-beam evaporation.

EXAMPLE 3 Growth of YSZ on Y2O₃ -buffered Ni and/or Cu by rf MagnetronSputtering

Initially, Y₂ O₃ films were grown epitaxially by e-beam evaporation onrolled-Ni substrated as described in Example 1. The YSZ films were grownon these Y₂ O₃ -buffered Ni substrates by rf magnetron sputtering. TheY₂ O₃ -buffered Ni substrate was mounted on a heating block inside thesputter chamber. Prior to heating the substrate, the sputter chamber wasevacuated to a pressure of 1×10⁻⁶ Torr. The chamber was then back-filledwith a flowing mixture of 4% H₂ and 96% Ar to a pressure of 5×10⁻² Torr.The substrate was heated to 780° C. for 15 min, and then the pressurewas reduced to 1×10⁻² Torr, and sputter deposited at about 780° C. for80 min with an on-axis YSZ target located 6 cm from the substrate. Theplasma power was 75 W at 13.56 MHz. The resulting YSZ film was smooth,and its thickness was estimated to be approximately 400 nm. Theaccompanying θ-2θ X-ray scan (as shown in FIG. 7) shows goodout-of-plane texture for the YSZ which is consistent with epitaxy. Fromthe ω as shown in FIG. 8) and φ (as shown in FIG. 9) scans for a 400 nmthick YSZ film grown on Y₂ O₃ -buffered Ni substrates, the FWHM for YSZ(200), and YSZ (220) are 9.5° and 11.7°, respectively.

The methods described in Example 3 can also be used to grow YSZ on RE₂O₃ -buffered Ni and Y₂ O₃ -buffered Cu as well as on alloys of Cu and/orNi and other metals and alloys which can be characterized by a surfacehaving biaxial texture by rf magnetron sputtering.

EXAMPLE 4 Growth of Yb₂ O₃ on Y₂ O₃ -buffered or CeO₂ -buffered Niand/or Cu by rf Magnetron Sputtering

Initially, Y₂ O₃ or CeO₂ films were grown epitaxially by e-beamevaporation on Rolled-Ni substrates as described in Example 1. The Yb₂O₃ films were grown on1 these Y₂ O₃ -buffered or CeO₂ -buffered Nisubstrates by ri magnetron sputtering. The buffered substrate wasmounted on a heating block inside the sputter chamber. Prior to heatingthe substrate, the sputter chamber was evacuated to a pressure of about1×10⁻⁶ Torr. The chamber was then back-filled with a flowing mixture of4% H₂ and 96% Ar to a pressure of 5×10⁻² Torr. The substrate was heatedto 780° C. for 15 min, and then the pressure was reduced to 1×10⁻² Torr,and sputter deposited at about 780° C. for 60 min with an on-axis Yb₂ O₃target located 6 cm from the substrate. The plasma power was 75 W at13.56 MHz. The resulting Yb₂ O₃ film was smooth, and its thickness wasestimated to be approximately 400 nm. FIG. 10 shows the θ-2θ X-ray scanfor a 400 nm thick Yb₂ O₃ on Y₂ O₃ -buffered Ni substrates. Theaccompanying θ-2θ X-ray scan for a 400 nm thick Yb₂ O₃ on CeO₂ -bufferedNi substrates (as shown in FIG. 11) shows good out-of-plane texture forthe Yb₂ O₃ which is again consistent with epitaxy. From the ω and φscans for the Yb₂ O₃ /CeO₂ /Ni film the FWHM for Ni (002), CeO₂ (002),and Yb₂ O₃ (002) are 12.2°, 8.20, and 10.7°, and that of Ni (111), CeO₂(111), and Yb₂ O₃ (222) are 10.30°, 8.70° and 8.7°, respectively. Fromthe XRD results, it can be concluded that Yb₂ O₃ can be grownepitaxially on Y₂ O₃ -buffered Ni and CeO₂ -buffered Ni substrates. TheYb₂ O₃ films were also grown epitaxially on YSZ/CeO₂ /Ni.

YBCO was then grown by pulsed laser deposition on three epitaxiallaminates of Yb₂ O₃ /CeO₂ /Ni, Yb₂ O₃ /YSZ/CeO₂ /Ni, and Yb₂ O₃ /Y₂ O₃/Ni. The typical YBCO thickness was about 300 nm for Yb₂ O₃ /CeO₂ /Niand Yb₂ O₃ /YSZ/CeO₂ /Ni, and about 400 nm for Yb₂ O₃ /Y₂ O₃ /Ni. Fromthe XRD results, the YBCO films grown on all architectures were found tobe epitaxial. The typical ω and φ scans for YBCO on Yb₂ O₃ /CeO₂-buffered Ni substrates with FWHM of 7.7° for YBCO (006) and 9.5° forYBCO (103) films are shown in FIGS. 12 and 13. The typical ω and φ scansfor YBCO on Yb₂ O₃ /YSZ/CeO₂ -buffered Ni substrates with FWHM of 6.5°for YBCO (006) and 8.9° for YBCO (103) films are shown in FIGS. 14 and15. The X-ray data (FIGS. 12-15) demonstrate the presence of a singletexture component of YBCO on Yb₂ O₃ layers as compared to that of twotexture components of YBCO grown directly on YSZ surface. The four proberesistivity plots showed a T_(c) (zero resistance) of 90-92 K for allthree films (FIGS. 16, 17 and 18). The transport criticalcurrent-density J_(c) was estimated to be 0.7×10⁶ A/cm² for YBCO/Yb₂ O₃/CeO₂ /Ni and 1.4×10⁶ A/cm² for YBCO/Yb₂ O₃ /YSZ/CeO₂ /Ni, and 0.8 A/cm²for YBCO/Yb₂ O₃ /Y₂ O₃ /Ni at 77° K and zero field. The temperature andmagnetic field dependence of normalized J_(c) of these superconductorsare shown in FIGS. 19 and 20. Also included are the data on films withYBCO deposited on standard YSZ/CeO₂ /Ni architecture for comparison. Ascan be seen from these figures that the performance of YBCO deposited onalternative buffer architectures as disclosed in the present inventionis similar to that of the standard RABiTS architecture, and demonstratethe presence of epitaxy and resulting strongly linked nature of thealternate buffer layers.

The methods described in Example 4 can also be used to grow Yb₂,₃ on Y₂O₃ -buffered or CeO₂ -buffered Cu as well as on alloys of Cu and/or Niand other metals and alloys which can be characterized by a surfacehaving biaxial texture by rf magnetron sputtering.

EXAMPLE 5 Growth of Gd₂ O₃ on textured-Ni Substrates by ReactiveEvaporation

An electron beam (e-beam) evaporation technique was used to deposit Gd₂O₃ films directly on Ni. The as-rolled Ni substrates were cleanedultrasonically with both acetone and methanol and recrystallized to thedesired (100) cube texture by annealing the substrates at 800° C. for 2hours in a vacuum of 10⁻⁶ Torr. Biaxially oriented Ni substrates weremounted on a substrate holder with a heater assembly in the e-beamsystem. After the vacuum in the chamber had reached 1×10⁻⁶ Torr at roomtemperature a gas mixture of 4% H₂ and 96% Ar was introduced until thepressure inside the chamber reached 1 Torr. The Ni substrates wereannealed at 700° C. for 1 hour at that pressure. The chamber was thenpumped and maintained at a pressure of 2×10⁻⁵ Torr using a mixture of 4%H₂ and 96% Ar. The gas flow was controlled by a dc-powered piezoelectricvalve. To understand the chemistry of the oxide formation, a DycorQuadruple Gas Analyzer was mounted in the e-beam system. The backgroundH₂ O pressure (pH₂ O) in the system was around 1×10⁻⁵ Torr. Thecrucibles used were usually graphite. Gadolinium metal was used as thesource. The Gd₂ O₃ layers were grown on the Ni substrates attemperatures ranging from 200 to 800° C. The deposition rate for Gd₂ O₃was 1-5 Å/sec with the operating pressure of 10⁻⁵ Torr, and the finalthickness was varied from 10 to 500 nm. during the deposition, the H₂ Opressure slowly fell to 4×10⁻⁶ Torr (when Quartz Crystal Monitor wasreading about 10 mn). The H₂ O was introduced into the system through avalve to maintain the H₂ O pressure around 1×10⁻⁵ Torr throughout thedeposition. This H₂ O pressure was sufficient to oxidize the film toform Gd₂ O₃ preferentially without oxidizing the Ni underneath. Also,just before the deposition, the Gd metal was evaporated for a fewseconds with the shutter closed. This was critical in changing thepartial pressure of from 10⁻⁷ Torr to 10⁻⁸ Torr. The Gd metal acts as anoxygen getter. The XRD results from the θ-2θ scan (as shown in FIG. 21),ω and φ scans for as-deposited Gd₂ O₃ (90 nm thick) on Ni at 700° C isas follows: The strong Gd₂ O₃ (400) from FIG. 21 revealed the presenceof a good out-of-plane texture. The FWHM for Ni (200) and Gd₂ O₃ (400)are 7.1° and 5.2° (FIG. 22), and that of Ni (111) and Gd₂ O₃ (222) are10.1° and 9.20° (FIG. 23), respectively. The Gd₂ O₃ (222) pole figurefor Gd₂ O₃ films grown at 700° C. on Ni is shown in FIG. 24. From theXRD results, it can be concluded that Gd₂ O₃ can be grown epitaxially onNi, Cu, and alloys thereof.

                                      TABLE 1                                     __________________________________________________________________________                         Melting                                                                             Temp. @ vap. pressure                              RE.sub.2 O.sub.3                                                                      Structure                                                                          a   a/2√2 or                                                                   point (RE)                                                                          10.sup.-6 Torr                                                                      10.sup.-4 Torr                               type    type (Å)                                                                           a/√2                                                                       data for pure metals (° C.)                       __________________________________________________________________________    Y.sub.2 O.sub.3                                                                       cubic                                                                              10.604                                                                            3.750                                                                             1509  973   1157                                         La.sub.2 O.sub.3                                                                      cubic                                                                              11.327                                                                            4.005                                                                             920   1212  1388                                         CeO.sub.2                                                                             cubic                                                                              5.411                                                                             3.827                                                                             795   1150  1380                                         PrO.sub.1.83                                                                          cubic                                                                              5.47                                                                              3.868                                                                             931   950   1150                                         Nd.sub.2 O.sub.3                                                                      cubic                                                                              11.08                                                                             3.918                                                                             1024  871   1062                                         Sm.sub.2 O.sub.3                                                                      cubic                                                                              10.927                                                                            3.864                                                                             1072  460   573                                          Eu.sub.2 O.sub.3                                                                      cubic                                                                              10.868                                                                            3.843                                                                             822   360   480                                          Gd.sub.2 O.sub.3                                                                      cubic                                                                              10.813                                                                            3.824                                                                             1312  900   1175                                         Tb.sub.2 O.sub.3                                                                      cubic                                                                              10.730                                                                            3.794                                                                             1357  950   1150                                         Dy.sub.2 O.sub.3                                                                      cubic                                                                              10.665                                                                            3.771                                                                             1409  750   900                                          Ho.sub.2 O.sub.3                                                                      cubic                                                                              10.606                                                                            3.750                                                                             1470  770   950                                          Er.sub.2 O.sub.3                                                                      cubic                                                                              10.548                                                                            3.730                                                                             1497  775   930                                          Tm.sub.2 O.sub.3                                                                      cubic                                                                              10.487                                                                            3.708                                                                             1545  554   680                                          Yb.sub.2 O.sub.3                                                                      cubic                                                                              10.436                                                                            3.690                                                                             824   590   690                                          Lu.sub.2 O.sub.3                                                                      cubic                                                                              10.390                                                                            3.674                                                                             1652        1300                                         (Y.sub.0.95 Eu.sub.0.05).sub.2 O.sub.3                                                cubic                                                                              10.604                                                                            3.750                                                        Y.sub.2 Ce.sub.2 O.sub.7                                                              cubic                                                                              5.370                                                                             3.798                                                        (Gd.sub.0.6 Ce.sub.0.4).sub.2 O.sub.3.2                                               cubic                                                                              10.858                                                                            3.839                                                        (Gd.sub.0.3 Ce.sub.0.7)O.sub.1.85                                                     cubic                                                                              5.431                                                                             3.841                                                        __________________________________________________________________________

The present invention clearly demonstrates the epitaxial growth of of Y₂O₃ and RE₂ O₃ layers on rolled-Ni and/or Cu substrates with or withoutadditional buffer layers. The present invention also demonstrates newsingle and multi-buffer layer architectures for high current YBCOconductors.

Further, processing conditions such as those described hereinabove maybe used to grow other buffer layers such as REAlO₃ (RE=Rare Earth),AEZrO₃ (AE=Ca,Sr,Ba), REZr₂ O₇ (RE=Rare Earth), Ca-stabilized Zirconia,Ti, Nb or Zr doped CeO₂, and AECeO₃ (AE=Ca,Sr,Ba) on rolled substrates.Other metallic substrates may also be used for growing these bufferlayers.

Various techniques which can be used to deposit these buffer layersinclude but are not limited to: physical vapor deposition techniqueswhich include electron-beam evaporation, rf magnetron sputtering, pulsedlaser deposition, thermal evaporation, and solution precursorapproaches, which include chemical vapor deposition, combustion CVD,metal-organic decomposition, sol-gel processing, and plasma spray.

While the preferred embodiments of the invention have been shown anddisclosed, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from thescope of the invention defined by the appended claims.

We claim:
 1. A biaxially textured article comprising:(A) a substratecomprising at least one metal, the substrate having a surface exhibitingbiaxial texture; and (B) a buffer layer selected from the groupconsisting of Y₂ O₃ and RE₂ O₃, the buffer layer being epitaxiallydisposed upon the biaxially-textured surface of the substrate.
 2. Thebiaxially textured article as described in claim 1 wherein the bufferlayer is a first buffer layer comprising Y₂ O₃, and the biaxiallytextured article further comprises:(C) a second buffer layer selectedfrom the group consisting of RE₂ O₃ and YSZ, the second buffer layerbeing epitaxially disposed upon the biaxially textured surface of the Y₂O₃.
 3. A biaxially textured article comprising:(A) a substratecomprising at least one metal, the substrate having a surface exhibitingbiaxial texture; (B) a first buffer layer comprising CeO₂, the firstbuffer layer being epitaxially disposed upon the biaxially texturedsurface of the substrate; and (C) a second buffer layer selected fromthe group consisting of Y₂ O₃ and RE₂ O₃, the second buffer layer beingepitaxially disposed upon the biaxially textured surface of the CeO₂. 4.A biaxially textured article comprising:(A) a substrate comprising atleast one metal, the substrate having a surface exhibiting biaxialtexture; (B) a first buffer layer comprising CeO₂, the first bufferlayer being epitaxially disposed upon the biaxially textured surface ofthe substrate; (C) a second buffer layer comprising YSZ, the secondbuffer layer being epitaxially disposed upon the biaxially texturedsurface of the CeO₂ ; and (D) a third buffer layer selected from thegroup consisting of Y₂ O₃ and RE₂ O₃, the third buffer layer epitaxiallydisposed upon the surface of the YSZ.
 5. A biaxially textured articlecomprising:(A) a substrate comprising at least one metal, the substratehaving a surface exhibiting biaxial texture; and (B) a buffer layercomprising (RE')_(x) O_(y), wherein x is about 2.0, and y is betweenabout 3.0 and about 3.7, the buffer layer being epitaxially disposedupon the biaxially textured surface of the substrate.